As the petroleum resources are disappearing rapidly, petrochemical products are consumed and environmental pollution is caused thereby, the whole world begins to pay attention to renewable wood biomass resources, mainly focusing on timber. Except for naturalness and renewability, the timber has many other advantages, for example, the timber is easy to machine, has a strength weight ratio higher than common metal materials, an air-seasoning material is a good thermal and electrical insulating material, the timber has an action of absorbing ultraviolet and reflecting infrared, and the timber is an elastoplastic material capable of regulating temperature and relieving dampness. Therefore, the timber must be an important research subject in future material science.
However, the timber is still mainly used for traditional industries such as papermaking. With the increase of global population, the amount of paper sheets consumed is also increased greatly. Due to the problem about a growth period of trees per se, the regeneration and utilization of the timber is also the priority among priorities.
The application of timbers mainly utilizes main stems of trees. Thus the barks and branches are abandoned and hardly utilized. Besides, in actual application, due to the use demands and the natural diameter of timbers are limited, all logs need to be machined, which inevitably causes the problems of timber shavings, etc. At present, the most direct method to solve the problem is to manufacture the timber into artificial boards, which usually requires adhesive and a high temperature thermo-pressing process. Even the adhesive-free artificial boards without the adhesive added inevitably needs to be manufactured by using a large-sized thermocompressor device under a high temperature thermo-pressing condition. Therefore, it is very important for the future development of the timber industry to manufacture the timer materials under an environment-friendly room temperature condition.
The main chemical components of the timber are substances forming cell walls and intercellular layers of the timber, and are formed by three high molecular compounds including cellulose, hemicellulose and lignin, and the total weight generally occupies more than 90% of the timber.
The separation technologies for the cellulose, the lignin and the like of the timber materials are mature. Therefore, it is very important to regain an available artificial timber by using the cellulose, semicellulose and the like.
An artificial timber is formed by extracting lignin from natural timber and winding around fibers utilizing the viscidity of the lignin to coagulate the fibers together. The obtained material has the prominent characteristics of easiness in molding, excellent performances, and capability of being decomposed in natural environment.
In order to reassemble the cellulose, the lignin and the hemicellulose into a whole macroscopic object, they can be dissolved and then assembled into a new timber product. Ionic liquid is an environment-friendly room temperature solvent, has better solubility for the cellulose and the lignin, and can dissolve them into a nanometer or even molecular level, which is more favorable for their reassembly and uniform coagulation. Meanwhile, recycling of the ionic liquid is also a mature technology. Therefore, it is a simple-to-operate and environment-friendly manner to use the ionic liquid to regain the available material from the cellulose and the lignin. The high temperature and high pressure conditions and usage of a large-sized thermocompressor device are also avoided. However, in prior art, the ionic liquid is used to dissolve the timber, but only an “aerogel” timber product can be prepared, and it is merely limited to low value products such as sound absorbing boards. So far, in the prior art, the ionic liquid dissolving technology has not been successfully applied in preparing a real artificial timber.
For the uniform system obtained by dissolving the cellulose and the lignin with the ionic liquid, a solvent replacement process needs to be used to remove the ionic liquid solvent. Usually, acetone-alcohol mixed solutions of different concentrations can be used for replacement and dissolving to finally obtain the timber products having a uniform fiber network. However, the materials obtained in such manner have a single structure and lower material strength and tenacity. There is no breakthrough for how to construct a multi-pore passage having a structure of enhanced particles in the field. Therefore, it is very important for constructing a high-performance artificial timber of a porous structure by determining a component ratio of raw materials and designing a reasonable replacement solvent system and conditions.